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%I #21 Sep 13 2022 02:20:41
%S 3,5,21,75,151,371,671,791,311,551,1271,1391,1031,2471,2231,4271,1991,
%T 3191,5351,7871,7751,7031,8951,8711,11831,5591,19631,10391,15791,
%U 20711,30071,17111,30551,27191,40031,31391,52631,49271,35591,42311,50951,92231
%N Least odd number k such that x' = k has n solutions, where x' is the arithmetic derivative (A003415) of x.
%C See A189559 for k restricted to prime numbers and A189558 for no restrictions on k.
%D See A003415.
%H Donovan Johnson, <a href="/A189560/b189560.txt">Table of n, a(n) for n = 0..200</a>
%F a(n) is the least odd k such that A099302(k) = n.
%o (Python)
%o from itertools import count
%o from sympy import factorint
%o def A189560(n):
%o if n == 0:
%o return 3
%o mdict = {}
%o for k in count(1,2):
%o c = 0
%o for m in range(1,(k**2>>2)+1):
%o if m not in mdict:
%o mdict[m] = sum((m*e//p for p,e in factorint(m).items()))
%o if mdict[m] == k:
%o c += 1
%o if c > n:
%o break
%o if c == n:
%o return k # _Chai Wah Wu_, Sep 12 2022
%Y Cf. A003415, A189558, A189559.
%K nonn
%O 0,1
%A _T. D. Noe_, Apr 24 2011
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